Lecture 25: Water Erosion

• Splash, sheet, rill, gully

Accelerated Soil Erosion and Land Degradation are Global Problems

• Large amount of croplands worldwide suffer from accelerated or unsustainable erosion
• Humans are the primary cause of erosion
• Cost of agricultural land degradation in Canada is 670$ million per year
• Our food quality is decreasing, less nutrients in soil, less in food
• Soil loss in the next 40 years in Africa can reduce crops by half

Soil Degradation Has Many Causes

• Soil degradation results from deforestation, agriculture, overgrazing, chemical contamination
• Over the past 50 years, soil degradation has become a major problem
• Grazing practices can contribute to soil degradation

Irrigation Boosts Productivity but can Cause Long-term Problems and Soil Degradation

• Groundwater depletion
• Water-logging
• Salinization - Build up of salts in surface soil layers
• Salinization inhibits production on 20% of all irrigated cropland, costing more than 11$ billion/yr

Problems with irrigation

• Expensive
• Alters root morphology
• Increase fungal pathogens
• Can cause salinity problems
• Subsidence

Remediating Soil Toxicity

• Salinity
• Soil PH
• Heavy metals

Phytoremediation

• Type of bioremediation (using living organisms to clean up contaminants)
• Phytoextraction
• Drawing chemicals up into plant biomass by action of plants that are hyperaccumulators
• Hydrangea is a hyperaccumulator of Aluminum

Desertification

• Loss of more than 10% productivity of arable land
• Can be natural or anthropogenic (accelerated desertification)
• Results from erosion, soil compaction, forest removal, etc...
• Semi-arid lands are most susceptible (where we live)
• Over-cultivation causes nutrient depletion

Dust Bowl was a Monumental Event in North American History

• Rapid mechanization
• Rapid conversion of grassland
• Poor agricultural practices

Soil Conservation Council Emerged from Experience of Drought

• National plan
• Communication

Crop Rotation

• Alternating the crops grown in a field from one season or year to the next
• Cover crops protect soil

Contour Farming

• Plowing furrows sideways across a hillside perpendicular to its shave to prevent runoffs

Terracing

• Cut into hills to form steps to hold water

Intercropping

• Planting different types of crops in alternating bands